As applications of the linear motion guide units grow in recent years to include the machinery working in increased operating severity, modern linear motion guide units increasingly need to work over a prolonged service life even under harshest atmosphere in which much foreign material including chips, debris, dirt, dusts, and so on occurs. Making sure of operation of the linear motion guide units in the harshest environment is first to keep the interior of the slider free of foreign materials or contaminants. Even with any invasion of outside foreign materials into the slider, the most significant issue is how to protect at least the circulating circuit including the load-carrying races to allow the rolling elements running through there against the foreign materials or contaminants. What's more, many of modern linear motion guide units are customized to have no conventional dustproof means including a telescopic cover, bellows, and so on despite laying their guide rails bare to the severe working atmospheres from the aspect of making the guide units themselves compact in construction, cost savings on installations, and so on while keeping the circulating circuits for the rolling elements free of the foreign material or contaminants.
A linear guide system is disclosed in Japanese Laid-Open Patent Application No. H07-301 232 in which there is provided a ball retainer with inner seals, which is composed of a rectangular metallic core plate coated with rubber or synthetic resins and made at forward and aft ends thereof with engaging parts in a way extending beyond the forward and aft ends in lengthwise direction of the core plate. On lengthwise side edges spaced away widthwise from one another, there are each provided a ball receiving-groove made curved in section, and an inner seal coming into sliding contact with both the top surface of the guide rail and the inward surface inside the slider facing on the guide rail. The ball retainer with inner seals is installed inside the recess in the slider with the forward and aft engaging parts coming into engagement with their mating recesses in the forward and aft end caps. The balls are charged into the load-carrying races after the installation of the ball retainer with inner seals.
However, the inner seals in the prior linear guide system as stated earlier, because of constructed to double as the ball retainer, is insufficient in sealing performance and therefore unfit for prolonged operation under the service severity as stated above. Moreover, the ball retainer with inner seals by itself would get larger in height in section and therefore couldn't fit the current demand to make the linear guide system compact or slim in construction.
Another linear motion rolling guide unit is disclosed in the commonly-assigned Japanese Patent No. 3 307 504 in which there is no need to disassemble the end caps away from the carriage to get an upper seal out of the slider. With the linear motion rolling guide unit envisaged as stated earlier, an upper seal placed inside a recess in the slider is made mounted and/or demounted easily out of a mortise cut into downward bulgy portion of the end cap, thereby helping shrink the linear motion guide unit in crosswise sectional height. With the prior linear motion rolling guide unit, the upper seal is made up of a core metal sheet with tenons at forward and aft ends thereof, and lip-type seals secured to side edges of the metal sheet. Once assembled, the lip-type seals come into abutment against their associated end seals. After having loosened screws to unfasten the end seals, the upper seal kept by them against lengthwise movement under duress is untied from the end seals to be allowed moving in longitudinal direction thereof. Lengthwise shift of the upper seal towards the untied end seal allows the opposing tenon to easily come out of the associated mortise. With the linear motion rolling guide unit constructed as stated earlier, thus, just loosening the screws tightened on the end seal is sufficient to disassemble the upper seal from the slider with no need of removal of the end caps from the carriage.
Nevertheless, it still remains a major challenge to develop the linear motion guide units with an inside seal installed within the slider, in which the inside seal is ensured in precious position control of sealing locations, smooth sliding contact of lip-type seals with the top surface of the guide rail, and in protection of the load-carrying races against foreign materials or contaminants that would otherwise creep between the top surface of the guide rail and the carriage and/or end caps of the slider, thereby keeping the load-carrying races free of foreign materials or contaminants.